Present day underwater breathing systems used by SCUBA divers consist of a tank containing a supply of air or other breathing gas at a relatively high pressure which initially exceeds 3000 p.s.i. Air is supplied to the diver at a pressure slightly grater than the pressure of the ambient water via a second stage demand regulator carried by the mouth of the diver whenever the diver inhales. Air from the tank is supplied to the second stage regulator at a constant intermediate pressure of about 140 p.s.i. via a first stage regulator mounted directly on the tank.
It has been observed that a diver's breathing effort increases as he or she descends in the water. Because the external pressure on the diver's body is proportional to the diver's depth, the lungs require constantly increasing air pressure during descent resulting in a constantly increasing air flow rate to the lungs. However, the air conduit passages in regulator systems are of fixed sizes, and therefore, as the air flow rate increases the pressure drops in the regulator system air conduit passages increase. As a result, breathing becomes more difficult as the depth of the diver increases since the diver must increase the suction effort to compensate for the increased regulator pressure drops.
Another disadvantage of present day first stage regulators arises from the fact that they are susceptible to icing and corrosion from the impurities contained in the ambient water, and that decreases the useful life of the regulators and increases the maintenance cost thereof.